Arthrodesis, also known as artificial ankylosis or syndesis, is a commonly used surgical procedure whereby two or more vertebrae are joined, fused or secured together to stabilize the spine. Arthrodesis may be done by itself, or in combination with other treatments such as decompression, in order to treat the pain that typically accompanies misalignment or instability of the vertebrae, such as spondylolisthesis, which can not be otherwise treated with pain medication, splints, or other normally-indicated treatments. Arthrodesis may also be done as a follow-up to decompression and debridement procedures that are performed to treat disorders such as spinal stenosis, herniated discs, spinal injuries, infection, tumors, and deformities.
Pedicle screw fixation has become an important part of stabilizing the spine to assist in arthrodesis. Pedicle screws do not fixate a vertebra or spinal segment themselves, but rather provide a means of gripping a vertebra and act as anchor points along a patient's spine that can then be connected with a rod or other stabilizing device. Traditionally, a significant amount of muscle dissection has been required to prepare for pedicle screw placement in the spine, which required longer surgical procedures as well as recovery times. Recently however, several alternative surgical approaches have been developed in an effort to minimize the amount of muscle dissection and unnecessary disturbance of paraspinous structures required in arthrodesis, while still accomplishing satisfactory placement of one or more pedicle screws and therefore fixation of the spine and the concomitant grafting necessary to achieve arthrodesis.
Once a surgical procedure opening the intermuscular planes to the spine has been performed, there are several options and methods that may be implemented to place a pedicle screw in the spine of a patient. For example, a retractor may be utilized by itself to locate and protect the pathway to a patient's spine for a conventional sequence of drilling and tapping, followed by placing a pedicle screw in the spine. While this approach is useful, it is typically more surgically invasive that other approaches. Alternatively, an awl may be used prior to surgery to palpate the bony surface and find the desired entry point to the patient's spine, with x-ray confirmation of position. Once the desired position is established, an incision is made through which the awl or seeker is tapped into the pedicle of the vertebral body, where the pedicle screw will be placed. However, this approach requires removal of the awl after tapping in order to place the pedicle screw in the bore created by the awl, which can result in a loss of position, with the entry point created for the screw being difficult to relocate.
Several devices, and combinations of devices, have been created to overcome the foregoing difficulties, such as those contemplated in U.S. Pat. No. 6,929,606 to Ritland and in U.S. Pat. No. 6,951,538, also to Ritland, both of which are incorporated by reference in their entirety. These devices utilize a combination of three separate instruments, a retractor, an awl, and an insert for the retractor through which the awl is placed and a bore created in the patient's spine, which is thereafter used to assist in the proper placement of a pedicle screw.